Various flange joining structures used for connection between fluid pipes have been proposed (see, for example, Patent Literatures 1 and 2), and various seal bodies for sealing have also been proposed (see, for example, Patent Literature 3). For example, in the flange joining structure disclosed in Patent Literature 1, a seal body, disposed between a flange portion of a first member (for example, a pipe member) and a flange portion of a second member (for example, a pipe member), includes a hard ring and a ring-shaped packing that is disposed on an inner circumference portion of the hard ring and, the hard ring is thinner than the hard ring. In the flange joining structure, when the first and the second members are joined to each other (fixed to each other through fastening with a bolt, a nut, and the like, for example) with the seal body sandwiched between the flange portions of the first and the second members, the hard ring has one surface in contact with an end surface of the flange portion of the first member and the other surface in contact with an end surface of the flange portion of the second member. Thus, the ring-shaped packing can be prevented from being excessively compressed, and thus compression exceeding an elastic limit can be prevented.
In the flange joining structure disclosed in Patent Literature 2, a seal body, disposed between a flange portion of a first member (for example, a pipe member) and a flange portion of a second member (for example, a pipe member), includes a ring-shaped packing main body and a plurality of compression limiting pieces that are embedded in the packing main body at an interval along a circumference direction. In the flange joining structure, when the first and the second members are joined to each other with the seal body sandwiched between the flange portions of the first and the second members, the plurality of compression limiting pieces limit the movement of the first and the second members toward each other, whereby the ring-shaped packing can be prevented from being excessively compressed.
The seal body disclosed in Patent Literature 3 is disposed between a first member (for example, a cylinder) and a second member (for example, a cylinder head), and includes a sealing annular body formed of an elastic material such as rubber and a ring-shaped reinforcement body that reinforces the sealing annular body. The ring-shaped reinforcement body is integrally provided to the sealing annular body by molding. The seal body has the ring-shaped reinforcement body increasing the rigidity of the sealing annular body, and thus prevents the sealing annular body from deforming (deforming at the time of replacing, deformation due to performance degradation, or the like).